> “Surely something is wanting in our conception of the universe. We know positive and negative electricity, north and south magnetism, and why not some extra terrestrial matter related to terrestrial matter, as the source is to the sink. … Worlds may have formed of this stuff, with element and compounds possessing identical properties with out own, indistinguishable from them until they are brought into each other’s vicinity. … Astronomy, the oldest and most juvenile of the sciences, may still have some surprises in store. Many anti-matter be commended to its care! … Do dreams ever come true?” -Sir Arthur Schuster, 1898, 34 years before the discovery of antimatter
Antimatter is some of the most wonderful stuff in the Universe. All of the normal matter on Earth — that you’re used to — is made up of atoms, which in turn are made of protons, neutrons, and electrons, like so.
But every particle that exists, whether it’s a fundamental particle (like a quark, electron, or photon) or a composite particle (like a neutron or proton), also has an antiparticle!
So what is an antiparticle?
In many ways, antiparticles are the same as regular particles. Same mass, same magnitude of charge, same magnitude of spin, and if you’re an unstable particle, you’ve got the same lifetime, too.
But there are a few very important differences! They have the opposite sign of charge, for instance. If a particle is positively charged (like a proton), its antiparticle (the antiproton) will be negatively charged. Neutrinos and antineutrinos, as another example, always have helicities (or spins, or intrinsic angular momentum, depending on your naming convention) opposite to one another. But the biggest one comes if you allow a particle to meet with its own antiparticle.
(Image credit: CSIRO; Australia’s version of the NSF.)
When a particle collides with its own antiparticle, they annihilate, and turn into pure energy via Einstein’s famous E = mc2, typically creating two ultra-high-energy photons.
It’s worth asking the question, what’s truly remarkable about this antimatter?
Sure, Tom Hanks can prevent you from blowing up the Vatican with it. But as a physicist, I can tell you with 100% certainty that antimatter, for us, is the most efficient source of energy in the Universe.
Let me explain, and let me start at the beginning. When you want to do something, it takes energy.
Whether you want to power a car, launch a rocket ship, or go for a walk, it takes energy to do it. Where does that energy come from? Well, regardless of whether you’re a car, a rocket, or a human being, this is the source of your energy.
That’s right, the plain old atom. The electrons orbiting your atoms store chemical energy. When the electron winds up in a lower energy configuration, it releases energy, and this is how everything from rocket fuel to TNT to the Krebs cycle to burning magnesium works: powered by atomic and molecular bonds.
Chemical energy — the kind that works by atomic transitions — is horrifically inefficient, however. If I bring about a million pounds of rocket fuel on board a ship, even if I have the best rocket fuel ever created, I can only turn about one pound of that fuel into energy, and I’m left with 999,999 pounds of waste. Yet, so far, this is the best we’ve been able to do as a fuel source, and this is currently how we power our rockets and spacecrafts.
But if we ever want to reach another star system, we’re going to have to do better. You already know of a better source of energy, you need look no further than this guy.
The Sun! That’s right, the Sun, rather than use chemical energy, relies on nuclear energy! Nuclear fusion, which fuses lighter elements into heavier ones (like the Sun), and nuclear fission, which splits apart heavy, unstable elements into lighter, more stable ones (like nuclear bombs or power plants), both are far more efficient than any form of atomic energy.
How much more efficient? If I had a million pounds of hydrogen, and I fused the entire million pounds into helium, how much would turn into energy, and how much would turn into (helium) waste? I’d get about 7,000 pounds worth of energy (which, by E=mc2, is a lot, but I’d still get 993,000 pounds of waste. 0.7% efficiency isn’t so great, all things considered.
But that’s where antimatter comes in. When we dream of interstellar spaceflight, we dream of a perfect fuel source. And if I brought a million pounds of fuel on board — 500,000 pounds of hydrogen and 500,000 pounds of antihydrogen — I’d get perfect efficiency: 1,000,000 pounds worth of energy and no waste.
(Yes, it takes much, much more than a million pounds of energy to make 500,000 pounds of antihydrogen, but that’s not the point.)
And that’s why creating and trapping neutral anti-hydrogen is such a big deal!
Sure, we’re a long way away from making half-a-million pounds of it, but this is the lightest, most stable form of antimatter we can make. And in principle, we can store an arbitrarily large amount of it for as long as we want.
This, no doubt, is the fuel of the long-term future. And while it’s way too early to start thinking about large, practical amounts of it anytime soon, this is the start of something that’s sure to be very, very big!
So if someone asks you what the big deal about antimatter is, you know what to tell them. Most. Efficient. Fuel source. Ever. In principle. And we just successfully stored it for the first time. So don’t be afraid to dream big; I know it’s what I’ll be doing!
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